A reader of characters on media having a variety of thicknesses is known in the art. The reader comprises a pair of rails spaced apart from one another and defining a maximum separation into which a medium is moved. The rails are secured to a wear plate, extending normal thereto and defining between them a channel in which the medium is placed. A read (and a write) head is positioned with respect to a first rail to detect the character as the medium is moved between the rails.
In order to accomodate media of different thicknesses, the spacing between the rails has to be adjustable. To this end, a platen is spring-loaded with respect to the first rail and biased into close proximity to the second rail to accomodate narrow media such as a check. The read (or write) head is suspended from the platen in a manner to permit independent adjustment and protrudes through a window in the platen. The spacing bewween the head and the opposing (second) rail on such a multimedia reader is maintained to 0.006"+/-0.001" in order to read OCR (optical character recognition) characters on media of a variety of thicknesses without causing an unacceptable amount of drag on the medium. The reader also has to be capable of reading magnetic characters thus creating the necessity for accurate spacing. It is clear that different relative positions are required for the heads, the platen and the rails for different media. The mechanical arrangements for ensuring that the different position requirements are met are typically costly, are difficult to set and in need of frequent adjustment. This is particularyy true of a head stop arrangement where a sensing head cannot be permitted to move outwardly to the extreme position occupied by a platen when a medium of maximum thickness is inserted between the rails. The head stop fixes the maximum movement of the head short of the maximum movement of the platen. The typical screw adjustment is almost inaccessible in the confines of close spaces available in such readers.